Pictorial review of Benedict XVI's last day a pope (photos)

German Economy Minister Philipp Roesler, Bavarian state governor Horst Seehofer and German Chancellor Angela Merkel, bottom from left, attend a thanksgiving service for outgoing pope Benedict XVI. at the St. Hedwig Cathedral in Berlin, Germany, Thursday, Feb. 28, 2013. At 8 p.m. sharp, Benedict will become the first pontiff in 600 years to resign. (AP Photo/Gero Breloer)

VATICAN CITY -- Pope Benedict XVI promised his "unconditional reverence and obedience" to his successor in his final words to cardinals Thursday, a poignant and powerful farewell delivered hours before he becomes the first pope in 600 years to resign.

In an unexpected speech inside the Vatican's frescoed Clementine Hall, the pontiff appeared to be trying to defuse concerns about possible conflicts arising from the peculiar situation of having both a reigning pope and a retired one.